Refrigeration systems capable of carrying out a cooling operation have been known in the art. In such a cooling operation, refrigerant is circuited so that, in a refrigerant circuit including a heat source side heat exchanger and a utilization side heat exchanger which are connected together, the heat source side heat exchanger functions as a condenser while the utilization side heat exchanger functions as an evaporator. This type of refrigeration system is used, for example, as an air conditioner for providing air conditioning of an indoor space by means of an indoor unit in which a utilization side heat exchanger is mounted.
JP-A-2006-71137 (hereinafter referred to as the “patent document”) discloses, as an example of such a type of refrigeration system, an air conditioner in which a compressor, an expander and an electric motor are connected together by a single drive shaft. The air conditioner of the patent document is configured such that the power resulting from the expansion of refrigerant in the expander is recovered and the recovered power is used to drive the compressor. A refrigerant adjustment tank is arranged downstream of the expander in the refrigerant circuit of the air conditioner. In a space cooling operation in which the refrigeration cycle is performed using an indoor heat exchanger as an evaporator, refrigerant in gas-liquid two-phase form exiting the expander flows into the refrigerant adjustment tank where the refrigerant is separated into liquid refrigerant and gas refrigerant. And the liquid refrigerant within the refrigerant adjustment tank is fed to the indoor heat exchanger.